This invention relates generally to methods and apparatus for detecting alignment of upper and lower teeth and more particularly to methods and apparatus for tracking the movement of the lower jaw relative to the upper jaw. There have been many types of jaw tracking devices developed for use in dentistry. They can generally be categorized as electromechanical devices and electro-optical devices.
Of the known prior art electro-optical devices used for jaw tracking, many employ reference points, either visually identifiable points or light emitting diodes, carried by frameworks attached to both upper and lower jaws and viewed by an externally mounted video camera. Most prior art electro-optical devices employ light emitting diodes carried by frameworks attached to the lower jaw and a video camera or other light sensing means attached to the head or upper jaw.
One problem with prior art electro-optical jaw tracking devices is that the frameworks by which the components are attached to the jaw or jaws must be custom fabricated for each patient and tend to interfere with natural jaw movements. The extraoral sensing means may either be attached or unattached to the patient. Unattached devices must be able to sense the positions of extraoral signal generating components or reference points attached to both upper and lower jaws. Attached devices must be attached to the patient's head or upper jaw by a framework affixed to the patient. Frameworks cemented onto the patient's teeth either cover the surfaces of the teeth and thereby alter the bite as well as the jaw movement pattern or must be custom fabricated for each subject in a way that allows them to fit around the teeth so as to avoid interfering with the bite. Such custom fabricated frameworks have been used for research, but they are too difficult to fabricate for routine clinical use. Furthermore, any framework that must extend through the lips interferes to some degree with neuromuscular proprioception and thereby also with natural jaw-movement patterns.
Another problem with prior art jaw tracking devices is that they cannot acquire data rapidly enough to track the minute deflections of the jawbone that are generated by inclined tooth contacts on many jaw closures. In 1980 Dr. David Watt published recordings of jaw tracking using a high speed camera to show that eccentric jaw closing trajectories frequently result in initial tooth contacts on steep inclines, which force the jaw to suddenly alter its direction and slide a fraction of a millimeter toward a more central position where subsequent multiple tooth contacts occur. D. Watt, Gnathosonic Diagnosis and Occlusal Dynamic. Furthermore, Dr. Watt showed that, during a single jaw closure, the jaw may change its direction more than once by striking multiple deflective tooth contacts before settling into a stable position. High speed cameras, like the one Watt used, are able to track jaw movements accurately if the lips are kept apart so that the cameras can track a point on an upper and a lower tooth. Keeping the lips apart, however, interferes with natural jaw movements much like frameworks do.
Most of the prior art devices track the movements of the jaw by means of charge coupled devices (CCD). However even a CCD screen cannot be scanned quickly enough to record the multiple rapid shifting of the jaw, which can occur in time frames of 10 to 50 milliseconds after an initial unstable tooth contact and before the final resting of the jawbone in stable interdigitation. Knowing the direction of slide of the jawbone after a deflective initial tooth contact helps determine which area of a tooth was actually hitting prematurely.
Another disadvantage with prior art jaw tracking devices is that they are not designed to be compatible with free head movement. Recently the use of miniature acoustic sensors has been developed to allow dentists to analyze and adjust a patient's bite. These sensors can determine which teeth hit first each time the jaw is closed. But the order of tooth contacts depends on the closing trajectory taken by the jawbone, and that trajectory varies a great deal within an area extending a couple of millimeters around the fully closed and maximally interdigitated jaw position. For example, if the jaw closes slightly to the right of the midline, the teeth on the right are likely to hit before the teeth on the left. In order for the dentist to accumulate enough tooth contact and jaw tracking data to create a map of these tooth contact patterns, known as the occlusal interface, the patient needs to be able to tap the teeth repeatedly while moving the jaw and the head into a wide variety of different postures. The prior art jaw tracking devices employ extraoral frameworks that interfere with the ability of the head and jaw to exhibit a normal and natural range of motion.
Still another disadvantage of all prior art jaw tracking devices is that they cannot be used with telemetry during sleep. Horizontal jaw tracking is needed during sleep to record the jaw positions used for nocturnal bruxism (grinding and clenching of the teeth). Many dentists believe that nocturnal bruxism is a common cause of dental problems. Studies have shown that nocturnal bruxism often occurs with forces that are significantly greater than even maximal voluntary forces while awake. Furthermore, there is evidence that much of nocturnal bruxism occurs in jaw positions that are shifted to the side, forward, or backward from the fully closed and maximally interdigitated jaw position. Knowing the horizontal jaw position in which a person's bruxism occurs allows a dentist to restore the teeth in a manner that can best resist the forces that arise during nocturnal bruxism. None of the prior art jaw tracking devices, however, can be used during sleep because they all employ frameworks that would interfere with sleep. The Journal of Oral Rehabilitation 1996 23: 622-626 recently published an account of an effort to record jaw position during sleep by means of a device that employed two magnetic reed switches. But the system of reed switches used was only able to approximate the position of the jaw, because each switch simply produced a signal if the magnet attached to the lower jaw on its side was closer than 2.65 mm from the switch.
Thus, it is an object of this invention to provide a jaw tracking device that is small enough to be located completely in the mouth without the need for any framework that extends through the lips.
It is a further object of this invention to provide a jaw tracking device that acquires data rapidly enough to record the direction of the very small slide of the lower jawbone during the time interval between the first tooth contact and subsequent tooth contacts.
It is a further object of this invention to provide a jaw tracking device that relies on few enough outputs so that they can be transmitted by telemetry during sleep without any need for wires coming out of the mouth.
It is a further object of the invention to provide a jaw tracking device that can be carried on existing removable dental appliances.